The present invention relates to a rotary shaft for a compressor.
Generally, a compressor of the closed type, for example, has a closed outer box in which electromotor and compressor sections are included. In addition, the outer box includes a rotary shaft which has a cylindrical rotary shaft body and an eccentric crank. A rotor in the electromotor section is secured to one end portion of the rotary shaft, and the eccentric crank is located in a compression chamber of the compressor section. An annular eccentric roller is fitted around the eccentric crank.
Conventionally, the eccentric crank is integrally formed, with the shaft body, or it is formed apart from the shaft body and is then secured to the shaft body by shrinkage fit, pressure fit, bonding or the like.
When the eccentric crank is integrally formed with the shaft body, it is made by casting or forging. Its materials are therefore limited in number and its manufacturing cost is substantially increased. When the eccentric crank is formed apart from the shaft body and is then secured to the shaft body by shrinkage fit, the dimensions of the rotary shaft may be changed, due to thermal influence, i.e., due to the residual stress caused by heating. In cases of pressure-fitting, there is the danger that the shaft body or eccentric crank might be deformed, damaging the outer circumference of the shaft body, as a result of resistance to the fitting pressure. In cases of bonding, the eccentric crank would be low in strength and lacking in reliability.
However, in the case of being separately formed, the cost is lower than in the case of being integrally formed. It is therefore desirable that a rotary shaft formed apart from the eccentric crank by provided, eliminating the disadvantages caused when the eccentric crank is secured to the shaft body.